The Augur was a priest or official in ancient Rome. His main role was take auspices: interpreting the will of the gods by studying the flight of the birds.
The position as augur was a very central one, as the Romans rarely did anything important without the consensus of the gods, as expressed in the auspices.
The ceremony of an augur "taking the auspices" was done before every public ceremony after Attius Navius impressed King Tarquinius. According to Livy, Tarquinius was involved in a Sabine war at the time. He thought he needed more cavalry to win, but he recalled a story about Romulus using an augur, so he thought he should do the same. He called on Attius, and asked him if he should add more cavalry. The answer was no, which upset Tarquinius. He was not convinced in the art of augury, so he asked Attius to do another, and to see if what he was thinking at the time was possible. The signs came back positive. Tarquinius thought he had Attius trapped, because what he had been thinking was that Attius should cut a whetstone in half with a razor. Attius did this immediately, and Tarquinius became a believer.